Cone beam artifacts are a well known problem in computed tomography. The X-ray source cone angle in most advanced CT systems such as Toshiba AquilionONE is quite large, and CFK images tend to suffer cone beam artifacts due to missing data in radon domain.
In one prior art approach, the artifact in circular cone beam CT is substantially removed by applying exact reconstruction based upon a theoretically complete trajectory such as a combination of a circular trajectory and a line trajectory. Although an additional line scan achieves a theoretically complete trajectory with a circular trajectory for exact reconstruction, the additional scan is often either unavailable or impractical to collect. Furthermore, since circular and line data are not simultaneously obtained, any change in motion or agent enhancement between the two scans causes data inconsistency between the two data sets and affect image accuracy. Lastly, the additional scan undesirably exposes a patient to an additional dose of radiation.
For the above reasons, it is of particular interest to accurately reconstruct image volume only from circular data. In another prior art approach, a scanogram is used to estimate line data. Although this approach does not increase patient's radiation dose, cone beam artifacts are still observable after the estimated line data generally helps reduce much of the artifacts. At the same time, any change in motion or agent enhancement is also causing some inaccuracy in the resulted images.
The above related patent application has disclosed another way to estimate the line data based upon a large image that is extended along a predetermined axis so that an improved image is reconstructed from the circular and the estimated line data. The large image also has a field of view (FOV) that is larger than a desired FOV and is extended in the Z direction to generate the extended large image. In reconstructing the improved image, although a scaling factor is optionally used, a value of the scaling factor has been determined prior to the reconstruction.
In the above described techniques, it is still desired to have additional improvement in a system and a method for substantially reducing artifacts in circular cone beam Computer Tomography (CT).